This invention relates to a lighting device.
Illuminants referred to as light diodes, light-emitting diodes or LEDs offer the possibility of producing flat light-emitting lampheads homogeneous over their surface, which in larger constructions as surface luminaires named “Softlight”, “Filllight” or lightener can be used in all fields of professional lighting, as portrait lamps in the direct vicinity of a motion picture or video camera, in confined spaces, such as vehicles and staircases, and for the erection of light walls for event or stage lighting.
From DE 20 2004 016 637 U1 a lighting device with a carrier is known, on which connection points for contacting electronic components and conductors are provided, which interconnect the connection points with each other and connect them with a power source. On the carrier, a light-emitting diode, a control electronic and switching devices for switching the light-emitting diode are arranged. The light-emitting diode in particular emits white light and is mechanically mounted on the carrier and in electrical contact with connection points. The control electronic contains a light sensor for measuring the ambient brightness and for regulating the brightness of the light-emitting diode, and includes a pulse width modulation circuit for controlling the intensity with which the light-emitting diode emits light.
When combining a plurality of such lighting devices, it is required to consider the specified radiation characteristic and actuation of each individual lighting device when determining the total characteristic of the expanded lighting device. In addition, due to the integration of a plurality of control electronics arranged on the carrier the known lighting device has a considerable space requirement, which in the case of a combination of a plurality of lighting devices for example to a lamphead would lead to considerable dimensions not acceptable in practice and the number of light-emitting elements would be too small for a lamphead because of the great mutual distance of the individual light-emitting diodes arranged on the carrier together with the control electronics and switching means. Therefore, an application of the known lighting device is limited to interior lightings of vehicles, light spots, reading lamps or the like.
Illumination lampheads with light-emitting diodes or LEDs, which are used for example as a camera attachment light for film and video cameras, either have the color temperature “daylight white” or “warm white”, wherein a stepless or exact activation or switchover from a warm white to a daylight white color temperature is not possible and in both variants the color rendering in film and video recordings is unsatisfactory.
When using LEDs of different colors with a non-continuous spectral distribution in an LED lamphead for the illumination of film or video recordings, the LEDs reach the required values for color temperature and color rendering, but when used for film recordings nevertheless have a considerable color cast as compared to incandescent lamps or HMI lamps or daylight. This is referred to as insufficient suitability for mixed light.
From EP 0 921 568 A2 a lighting device is known, in which a plurality of LED chips emitting monochromatic light of different colors are inserted into depressions of a three-dimensional carrier of rectangular cross-section, are electrically connected with conductors and sealed with a transparent plastic material. In emission direction of the LED chips, a diffuser plate of transparent plastic material, which consists of microlenses for light control, is connected with the three-dimensional carrier. The matrix-like combination of a plurality of modules with LEDs emitting monochromatic red, green, blue and yellow light with different color mixture and light scatter, which are arranged in the depressions of the carrier, leads to a lighting device with adjustable light color and light scatter.
In this lighting device of matrix-like construction, the total characteristic of the light emitted by the lighting device also is determined by the individual light modules arranged in the depressions of the three-dimensional carrier, i.e. when changing individual modules, the total characteristic of the lighting device must be newly determined. Since individual properties as regards color characteristic and light scatter are assigned to the individual modules of the lighting device, the total characteristic of the light emitted by the lighting device can be varied considerably in the case of the failure of individual modules.